The present disclosure generally relates to semiconductor devices, and more particularly to the fabrication of magnetic memory devices.
A recent development in semiconductor memory devices involves spin electronics, which combines semiconductor technology and magnetics. The spin of electrons, rather than the charge, is used to indicate the presence of a “1” or “0.” One such spin electronic device is a magnetic random access memory (MRAM) device which includes conductive lines (wordlines and bitlines) positioned in a different direction, e.g., perpendicular to one another in different metal layers, the conductive lines sandwiching a magnetic stack or magnetic tunnel junction (MTJ), which functions as a magnetic memory cell. A current flowing through one of the conductive lines generates a magnetic field around the conductive line and orients the magnetic polarity into a certain direction along the wire or conductive line. A current flowing through the other conductive line induces the magnetic field and can partially turn the magnetic polarity, also. Digital information, represented as a “0” or “1,” is storable in the alignment of magnetic moments. The resistance of the magnetic memory cell depends on the moment's alignment. The stored state is read from the magnetic memory cell by detecting the component's resistive state.
An advantage of MRAM devices compared to traditional semiconductor memory devices such as dynamic random access memory (DRAM) devices is that MRAM devices are non-volatile. For example, a personal computer (PC) utilizing MRAM devices would not have a long “boot-up” time as with conventional PCs that utilize DRAM devices. Also, an MRAM device does not need to be powered up and has the capability of “remembering” the stored data. Therefore, it is expected that MRAM devices will replace flash memory, DRAM, and static random access memory devices (SRAM) devices in electronic applications where a memory device is needed.
Because MRAM devices operate differently than traditional memory devices, they introduce design and manufacturing challenges. The magnetic material layers used in MRAM devices require different etch chemistries and processes than traditional materials used in semiconductor processing, making them difficult to integrate into MRAM manufacturing processing schemes. For example, because of their small z-direction thickness, MTJ freelayers are expected to require gentler etching solutions than typical microelectronic back end of line processes or utilize thicker films to minimize lateral etching and to maximize etching selectivity with respect to thin tunneling barrier, which are commonly fabricated from a metal oxide such as AlOx, and the like.
The simplest case of tunnel barrier dissolution may be written as:RTot=RH++RL the linear combination of proton-promoted (RH+) and anion/ligand-promoted (RL) dissolution reactions, assuming these reactions are independent and parallel. Typically RL will depend not only on the surface concentration of ligand, but also on the type; for example, a 5- or 6-membered ring forming chelate will promote higher rates of metal oxide dissolution than one which forms chelate rings of fewer or more than 5 or 6. The simplest way to reduce RL to close to zero is to choose an acid with a non-surface interacting ligand, and to use pure solutions.
In the past, ultrapure perchloric acid HClO4 has been the acid of choice where a non-adsorbing acid anion was used. However, due to safety considerations, HClO4 has fallen out of favor; there is also the possibility of chloride contamination in HClO4 solutions.
Accordingly, there is a need for improved etching processes for removing selected portions of the magnetic layer disposed on the tunnel barrier.